This disclosure relates to systems using Fibre Channel devices wherein while new devices can be added or removed to the system but this incurs a disruption and an exception condition which is caused, which then requires specialized handling.
Many systems are connected to remote peripheral devices such as tape controllers and disk units via Fibre Channel optical cable for the purpose of writing and storing data and also for the purpose of reading back data.
Fibre Channel involves a type of transmission path often used as an internal computer channel as well as a network medium for transmission. It works with existing interfaces such as IPI, SCSI, and certain other interfaces. In a local area network, it can be used as a high-speed data transmission medium. It provides for speeds ranging up to a hundred megabytes per second with use of optical fibre.
Packets of information can be transferred from a computer platform through a Fibre Channel host bus adaptor while carrying an address which will transport a packet of data to a given tape controller or to a particular disk unit.
Under normal operations, there is a standard transmittal of data from the computer platform over to the designated tape controller or disk unit as long as the network stays stable with the same number of peripheral units and no changes have been made.
However, should a tape controller be added to the network fibre optic cable channels or should a new disk unit be added and connected through fibre optic cable to the platform, this completely changes the operating situation and leads to transmission completion problems, since the interruption to the status quo has now changed the conditions of operation so that the transmission loops for carrying the data may no longer be operable.
Thus, in those situations where a peripheral such as a tape controller was added in, this injected an element of confusion and interruption to the transmission loop, which often resulted in the lack of proper completion of data transmission.
MASTER CONTROL PROGRAM (MCP): This denotes the operating system software that is used to operate on a ClearPath platform which is a Unisys Corporation computer system.
INPUT/OUTPUT CONTROL BLOCK (IOCB): The Input/Output Control Block is a data structure used by the Master Control Program (MCP) to describe all the information needed to issue a Input/Output command to another device. This will include the (i) destination unit; (ii) the pointer to the data being transferred; (iii) the length of the Input/Output data; (iv) the Result Description which describes the outcome of the Input/Output operation to indicate whether it was in error or properly completed.
INPUT/OUTPUT MODULE (IOM): This is a particular module of a ClearPath system that is responsible for initiating and completing Input/Output operations from the Master Control Program (MCP) to a peripheral and/or vice versa.
FIBRE CHANNEL HOST BUS ADAPTER: This is a particular unit of a ClearPath computer system that is responsible for communicating on the Fibre Channel Loop.
MEMORY: This is the particular memory module of the ClearPath System that allows access to the E-Mode Memory of the Unisys Platform. This is the memory that is used by the operating system and all of its sub-modules.
PACKET ADDRESS UNIT: This is also called a Command Packet. This is a data structure used by the Input/Output module (IOM) and the CMU in order to transfer data for an I/O request from the host. This packet sustains much of the same characteristics that is done by the IOCB, except that this packet structure is used between the IOM, the CMU, and the Channels. In particular, this structure has an actual physical device which is to be communicated with.
HUB: This is the industry standard definition of a multi-connection black box. This device takes a Fibre Channel signal and propagates it to the next port in the box. Some Hubs have eight ports and some have sixteen and are manufactured by several different companies. Sometimes more than one Hub is used in a network because these devices allow greater connectivity.
TAPE CONTROLLER: This is the mechanism which controls and records and writes on the magnetic tape units which are used to write and store data which can be read out for later utilization.
FIBRE CHANNEL OPTICAL CABLE: This is the industry standard optical cable that carries the input and output lines of the Fibre Channel signal. It is used to connect one Fibre Channel device to another.
TAPE UNITS: In this context, these are Fibre Channel tape devices. In the present embodiment, this utilizes the CTS9840-FC Tape Drive from STK (Storage Tech Corporation).
DISK UNITS: These indicate Fibre Channel disk devices used for the recording, writing and reading of data.
FC ARBITRATED LOOP: This is a Fibre Channel Arbitrated Loop which is the encompassing configuration depicted with an initiator (the FC Channel HBA) and several targets, such as the tape and disk devices. HBA refers to the Host Bus Adapter.
INPUT/OUTPUT RESULT DESCRIPTOR (IORD): This is the information return from an Input/Output operation that describes any exceptions that occurred in the life of that particular Input/Output operation.
STILLBORN: This is a term given to an Input/Output operation that was intended to be initiated to a device, but thereupon an exception occurred before the Input/Output could get out to the device, thus causing the Input/Output operation to be returned back to the host without ever being received by the intended device.
TAPE EXCEPTION: This is the result signal of an Input/Output operation that is issued to a Tape Device, wherein that Tape Device has encountered a problem and returns an error signal for that particular Input/Output operation. In the present case, the tape exception would be designated as an OUTBOARD BUS RESETxe2x80x94this is otherwise known as a LIP or Loop Initialization Procedure.
LOCATE COMMAND: This is a SCSI tape command that moves the current logical position on the tape peripheral to a new position on the tape as specified by the information passed in this particular command.
READ POSITION COMMAND: A SCSI tape command that reports the current logical position of the drive, but does not cause any tape motion to occur.
TIMEOUT PROCEDURE: This is the procedure that determines how to handle an Input/Output operation (I/O) that has developed an xe2x80x9cexceptionxe2x80x9d which is designated as HANDLEMAGTAPEEXCEPTION.
TERMINATE I/O: This is a procedure designated TERMINATEIOOPERATION whereupon this procedure gets the initial I/O result back from the Input/Output module (IOM). It then processes the Result Descriptor to determine if this Input/Output can be quickly retried or whether it must be handled by the HANDLEMAGTAPEEXCEPTION.
OUTBOARD BUS RESET: The Fibre Channel Host Bus Adapter returns a signal called the Outboard Bus Reset when an input operation was incapable of being completed to its intended recipient.
UNIT NUMBER: This is a number given to a peripheral device so that it can be identified by the system.
FIBRE ADDRESS: This is the address needed for the Fibre Channel Host Bus Adapter (HBA) to deliver the Fibre Channel package to the designated peripheral device.
LIP RESULT (LOOP INITIALIZATION PROCEDURE RESULT): This is a Result Descriptor which is returned by the Input/Output unit to the Master Control Program (MCP) that signifies that a Loop Initialization Procedure has occurred (transmission interrupted) during that particular Input/Output operation. This result is also described as xe2x80x9cOutboard Bus Resetxe2x80x9d whenever it is displayed.
LIP INITIATION (LOOP INITIALIZATION PROCEDURE INITIATION): Whenever a fibre device on the loop is added into the loop or if something catastrophic occurs to the device and it needs to get cleared, then a Loop Initialization Procedure (LIP) is initiated.
DATA TRANSFER I/O: This is a SCSI/fibre command which causes data to be transferred along the interface. These commands would include such things as a Write or a Read command.
LOOP INITIALIZATION PROCEDURE (LIP): A Loop Initialization Procedure is initiated when a device is added onto the fibre loop or if one of the peripheral devices is xe2x80x9chungxe2x80x9d and needs to be reset back to its original state. This resetting is done by causing a Loop Initialization Procedure which in turn, causes all devices in the loop to re-identify themselves on the loop.
CHANNEL MANAGER UNIT (CMU): This is an in-between intermediary section of the I/O subsystem. Every channel manager unit has 4 channels, so that the flow of an I/O really goes from the IOM to the CMU and then to the channel.
TERMINATEIOOPERATION: This is a procedure which takes place after the occurrence of a Loop Initialization Procedure and works to handle the Input/Output operation.
THE DISPLAY COMMAND: This is a command used to display an ASCII character string in the display panel of the tape device.
REWIND COMMAND: This is a command that causes the tape to be rewound to the logical beginning of the tape.
TEST COMMAND: This command provides a means for determining if the tape is ready to accept an appropriate medium access command.
In a system where a computer platform controls and organizes data for transmission to selected peripheral units such as tape controllers and disk units, provision is made for use of a Fibre Channel host bus adapter which can transfer the packets via Fibre Channel optical cable to a Hub which can then route the data packets over separate optical cable to different destinations, such as a specifically addressed tape controller or a specifically addressed disk unit.
However, when a new peripheral is added to the Fibre Channel optical loop or if a peripheral is removed, this causes an unsettled situation where the Fibre Channel loop, designated as a Fibre Channel arbitrated loop, no longer recognizes the earlier group of peripherals and must be reconstituted and set up to recognize the new state of peripheral devices which are connected to the fibre optic loop.
In this situation, a Loop Initialization Procedure (LIP) is instituted which then attempts to reconstitute the loop after the disruption. Thus, any Input/Output operations previously issued to a tape or disk device will now have to be recovered.
At the moment of the disruption, if the I/O operation has not yet been issued to the peripheral device, then the Input/Output processor signifies this by initiating a Result Descriptor which informs the computer platform. And in this case, the Master Control Program (MCP) of the computer platform will retry this particular Input/Output operation.
However, if the I/O operation has already been issued to the device, and during the transmission is informed that a Loop Initialization Procedure has occurred which indicates that there has been a reconstitution of the peripherals from what was previously in operation, then the Master Control Program (MCP) of the platform will determine what particular kind of Input/Output operation was issued and reissue the Input/Output operation if this is possible.
However, if the Input/Output operation was a command which was in transition but whereby it could not be determined what the position of the tape head was at the time of the Loop Initialization Procedure, then the input operation has to be considered as failed and determined to be non-recoverable, and this is indicated in a Result Descriptor which is fed to the computer platform.